Original recipe from http://foodinjars.com/2009/08/blackberry-jam/
Yield: Approximately 3 Pints
6 cups blackberry pulp (8-9 cups of berries, mashed through a strainer with the back of a wooden spoon)
4 cups sugar
2 teaspoons cinnamon
1 teaspoon freshly grated nutmeg
1 lemon, juiced and zested
1 packet liquid pectin (half the box)
Prepare your jars, start your lids to simmering and bring your canning pot to a boil.
In a large, non-reactive pot (stainless steel or enameled cast iron), combine the sugar and fruit pulp and bring to a simmer. Add cinnamon, nutmeg and lemon zest/juice and stir to combine.
Let the mixture reach a boil, stirring frequently to prevent it from boiling over. When the mixture appears to be thickening a bit, add the pectin and bring it back to a roiling boil.
Let it boil vigorously for at least five minutes to activate the pectin. Before removing from the heat, check the set using the plate or spoon test to ensure that the jam will firm up when cool.
Fill your jars with the hot jam, wipe rims, apply lids and rings and process in a boiling water canner for ten minutes.
Remove from canner and allow the jars to completely cool on a dishtowel-lined counter top.
Once the jars are cool, check the seals, label them.